Bicycle front sprocket

ABSTRACT

Methods and apparatus for a composite bicycle front sprocket are disclosed herein. One embodiment discloses a composite bicycle front sprocket assembly having an outer assembly of a first material. The bicycle front sprocket assembly also has a center assembly of a second material. The center assembly is disposed at least partially within the outer assembly. The center assembly is irremovably coupled with the outer assembly. The center assembly is irremovably coupled with the outer assembly without an external fastening device to irremovably couple the center assembly with the outer assembly.

CROSS REFERENCE

This application is a divisional of and claims the benefit of and claimspriority to co-pending U.S. patent application Ser. No. 15/485,009,filed on Apr. 11, 2017, entitled “BICYCLE FRONT SPROCKET” by Robert ErikMoore et al., assigned to the assignee of the present application,having Attorney Docket No. FOX-P4-11-16-US, and is hereby incorporatedby reference in its entirety.

The application Ser. No. 15/485,009 claims priority to and benefit ofU.S. Provisional Patent Application No. 62/321,138 filed on Apr. 11,2016, entitled “Composite Chain Ring” by Robert Erik Moore and assignedto the assignee of the present application, having Attorney Docket No.FOX-P4-11-16-US.PRO, the disclosure of which is hereby incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

Embodiments of the invention generally relate to a front sprocketassembly for a chain driven vehicle.

BACKGROUND

Traditional bicycle front sprocket structures are often made frommetals, such as aluminum. Moreover, it is presently a subtractiveprocess to make them. For example, the metal is machined, punched out,stamped, and the like.

The traditional bicycle front sprocket is also a relativelyflat-structure. In other words, the current front sprocket is like aplate or disc, e.g., a 2-dimensional structure, which results in ithaving low lateral stiffness. In a bicycle, such as a mountain bike thathas a large number of gears in the rear, there can be a significantamount of cross-chaining. E.g., the angle of the chain changes as thedifferent rear gears are selected. As the chain moves to the peripheralgears on the rear, there can be an increasing component of lateral pullon the front sprocket which can deleteriously affect the traditionalfront sprocket, resulting in a loss of drive efficiency and potentialfor mechanical issues.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present invention are illustrated by way of example, andnot by way of limitation, in the accompanying drawings, wherein:

FIG. 1 is an exploded view of a crack assembly, in accordance with anembodiment.

FIG. 2 is a diagram of a bicycle front sprocket assembly, in accordancewith an embodiment.

FIG. 3 is a transparent diagram of the bicycle front sprocket assembly,in accordance with an embodiment.

FIGS. 4A, 4B and 4C are different views of the crank drive ring, inaccordance with an embodiment.

FIGS. 5A, 5B and 5C are different views of the composite bicycle frontsprocket assembly, in accordance with an embodiment.

FIGS. 6A, 6B, 6C, 6D, 6E and 6F are different views of the outerassembly, in accordance with an embodiment.

FIG. 7 is a flowchart of a method for manufacturing the bicycle frontsprocket assembly, in accordance with an embodiment.

FIG. 8 is a flowchart of a method for manufacturing the bicycle frontsprocket assembly that includes a crank drive ring, in accordance withan embodiment.

The drawings referred to in this description should be understood as notbeing drawn to scale except if specifically noted.

DESCRIPTION OF EMBODIMENTS

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various embodiments of thepresent invention and is not intended to represent the only embodimentsin which the present invention is to be practiced. Each embodimentdescribed in this disclosure is provided merely as an example orillustration of the present invention, and should not necessarily beconstrued as preferred or advantageous over other embodiments. In someinstances, well known methods, procedures, and objects have not beendescribed in detail as not to unnecessarily obscure aspects of thepresent disclosure.

In one embodiment of the front sprocket assembly described hereinachieves a more integrated aesthetic with composite crank arms.Additionally, embodiments create a front sprocket assembly which islighter than all-aluminum front sprocket. Further the bicycle frontsprocket assembly is able to achieve the above accomplishments whilestill meeting or exceeding conventional strength and stiffness criteriafor front sprockets. Also, the disclosed front sprocket assembly can bebuilt with a lower cost than is found in many conventional frontsprockets. The lower costs include a material savings provided by aprocess that reduces material waste when compared to a traditionalmanufacturing process.

FIG. 1 is an exploded view of a crank assembly 10, in accordance with anembodiment. In one embodiment, crank assembly 10 is shown in conjunctionwith bicycle frame and bottom bracket portion 11 where it is mounted.Crank assembly 10 includes a left hand non drive crank assembly 34 whichincludes a left hand crank arm 15 b and a spindle 12. Crank assembly 10also includes a right hand drive side crank assembly 36 which includes aright hand drive side crank arm 15 a and a front sprocket assembly 100.In one embodiment, spindle 12 includes a spindle interface 13.

During assembly, right hand drive side crank arm 15 a has an assemblyinterface 17 that will couple with front sprocket assembly 100. Frontsprocket assembly interface 17 will couple with opening 109 of frontsprocket assembly 100 (as shown in FIG. 2) to fixedly couple frontsprocket assembly 100 with right hand drive side crank arm 15 a therebyforming the right hand drive side crank assembly 36. In one embodiment,after front sprocket assembly 100 is coupled with right hand drive sidecrank arm 15 a, a lock ring is used to fixedly couple the front sprocketassembly 100 onto right hand drive side crank arm 15 a.

Spindle 12 is inserted through bicycle frame portion 11 and spindleinterface 13 couples with the interface on right hand drive side crankassembly 36. In one embodiment, crank assembly 10 includes additionalparts such as, pedals, pedal washers, preloader, dust caps, spindlespacers, bearings, hex nuts, preload adjusters, and the like. Thoseparts are not shown for purposes of clarity.

With reference now to FIG. 2, a diagram of a front sprocket assembly 100is shown in accordance with an embodiment. Front sprocket assembly 100includes an outer assembly 102 having a plurality of teeth 104 about anouter perimeter. In one embodiment, outer assembly 102 has 32 teeth.Although 32 teeth are shown in one embodiment, the technology is wellsuited to the use of various other numbers of teeth 104 such as 28, 30,34, or the like. In one embodiment, outer assembly 102 is comprised of afirst material. In one embodiment, the first material is a metalliccomponent, e.g., aluminum, titanium, steel, or the like.

Front sprocket assembly 100 further includes a center assembly 106. Inone embodiment, center assembly 106 is comprised of a different materialthan that of outer assembly 102. In one embodiment, center assembly 106is formed by injection molding of carbon fiber reinforced nylon. Inanother embodiment, center assembly 106 is formed via compressionmolding. In yet another embodiment, center assembly 106 is formed viacomposite layering. In one embodiment, the material for center assembly106 is nylon reinforced with carbon fibers. In other embodiments, thematerial for injection molded center assembly 106 is chopped carbonfibers. In yet another embodiment, center assembly 106 may be a plastic,polymer, other long fiber-reinforced plastics, or the like.

In one embodiment, center assembly 106 is formed with an optional crankarm fitting area 112. In general, crank arm fitting area 112 is anindentation formed in center assembly 106 within which right hand driveside crank arm 15 a will fit.

Center assembly 106 has an opening 109 in the center thereof. Opening109 is provided for coupling front sprocket assembly 100 with right handdrive side crank arm 15 a via front sprocket assembly interface 17.Opening 109 further allows the insertion of spindle 12 there throughsuch that spindle interface 13 can be coupled with right hand drive sidecrank assembly 36.

In one embodiment, the first material forming outer assembly 102 isselected to have a modulus of elasticity which is higher than themodulus of elasticity of the second material which forms center assembly106. In one embodiment, the first material is aluminum, titanium, steel,or another metal; and the second material is a composite material suchas, for example, carbon fiber reinforced plastic material, plastic,polymer, fiberglass, or the like.

In one embodiment, front sprocket assembly 100 includes optional crankdrive ring 108. In one embodiment, crank drive ring 108 is coupled tocenter assembly 106 such that crank drive ring 108 is disposedapproximately about a center of outer assembly 102 surrounding opening109.

In one embodiment, crank drive ring 108 is used to transfer the loadduring high pressure situations, and to stop brinelling that may occurin the composite material of center assembly 106 along the splineinterface and marring about opening 109. In one embodiment, the crankdrive ring 108 is made of the same material as outer assembly 102. Inanother embodiment, the crank drive ring 108 is made of a differentmaterial such as titanium, steel, or other metal or composite. In oneembodiment, crank drive ring 108 is ceramic. For example, a ceramicco-mold may be used to mold a ceramic crank drive ring 108 within theinjection mold process.

Referring now to FIG. 3, a transparent diagram of front sprocketassembly 100 is shown in accordance with an embodiment. In FIG. 3, tabs110 are formed during the formation of outer assembly 102 and areinwardly projecting from outer assembly 102.

As shown in FIG. 3, in one embodiment, center assembly 106 is coupled toouter assembly 102 utilizing tabs 110 of outer assembly 102 such thatcenter assembly 106 is formed about tabs 110 of outer assembly 102. Inone embodiment, tabs 110 are tapered such that they are narrower at thebase of outer assembly 102 and wider at the furthest point from outerassembly 102. As such, the center assembly 106 will lock about the tabs110 of outer assembly 102 and resist having outer assembly 102 frombeing pulled out of the center assembly 106.

In one embodiment, one or more tabs 110 will include an optional hole187. In general, optional hole 187 is at least one opening through tabs110 that are utilized during the molding process to provide additionalsecurity in the contact between outer assembly 102 and center assembly106. By having the center assembly 106 flow around tabs 110 and throughhole 187 during the formation of front sprocket assembly 100; the finalfront sprocket assembly will have additional contact areas andinterlocking aspects to further keep center assembly 106 properlyoriented and fixedly and irremovably coupled with outer assembly 102.Moreover, due to the center assembly 106 being formed about outerassembly 102, the components will be irremovably coupled without anyneed for an external fastening device such as, but are not limited to:screws, bolts, clips, rivets, and the like.

Although four tabs 110 and four spokes for center assembly 106 areshown, the use of four spokes and tabs is an industrial design concept.It should be appreciated that center assembly 106 may have any number ofspokes and that outer assembly 102 may have any number of tabs 110. Forexample, in another embodiment, composite center assembly 106 isirremovably coupled with two or more of the plurality of tabs 110 on theinner perimeter of outer assembly 102. Further, the number of spokes forcenter assembly 106 and tabs 110 of outer assembly 102 may not always bethe same. For example, outer assembly 102 could have 6 tabs 110 andcenter assembly would only have four spokes and thus only utilize fourof the tabs 110.

In one embodiment, because of the injection molding process, the spokesof center assembly 106 will overlap with the tabs 110 of outer assembly102 but will not connect with each other. By not having the centerassembly 106 wrapping around the entire inner circumference of outerassembly 102 (e.g., a circular perimeter), knit lines can be avoidedduring the injection molding process.

However, in another embodiment, center assembly 106 may be manufacturedvia composite layering or the like which would allow center assembly 106to have a continuous perimeter about outer assembly 102 without theconcern of knit line formation.

With reference now to FIGS. 4A, 4B and C, three different views of crankdrive ring 108 are shown in accordance with one embodiment. FIG. 4A is afront view 400, FIG. 4B is a side view 425 and FIG. 4C is a isometricview 450.

The inner diameter of crank drive ring 108 includes a geometry thatcorresponds to the shape of front sprocket assembly interface 17. Theouter diameter of crank drive ring 108 has an array of block features401 that are surrounded by partial holes 415 which are slightlyover-center to create a tapered shape on the block features 401 thatacts similar to a shrink fit for locking the crank drive ring 108 intothe composite center assembly 106.

In one embodiment, crank drive ring 108 is made from aluminum (or othermetal). During the manufacturing process, center assembly 106 is moldedabout the tapered shaped block features 401 of crank drive ring 108 (andsimilarly the tapered shaped block features of tabs 110 of outerassembly 102). When the carbon fiber and aluminum are molded together attemperate, there is a difference between the thermal expansion ofaluminum (or other metal making up crank drive ring 108) versus thethermal expansion of carbon fiber (or other material making up centerassembly 106). Since the aluminum (or other metal) has a higher thermalexpansion, during the cooling process the aluminum contracts more thanthe carbon fiber. As such, the block features 401 that are surrounded bypartial holes 415 will shrink more than the carbon fiber center assemblywhich will further fixedly and irremovably couple the aluminum crankdrive ring 108 with the carbon fiber center assembly 106 without anexternal fastening device being needed. Examples of an externalfastening device include, but are not limited to: screws, bolts, clips,rivets, and the like.

With reference now to FIGS. 5A, 5B and 5C, three different views of thefront sprocket assembly 100 are shown in accordance with an embodiment.FIG. 5A is a front view 500, FIG. 5B is a side view 525 and FIG. 5C is across sectional view 550. FIG. 5A front view 500 is similar to that ofFIG. 2 and is utilized to illustrate the cross section FIG. 5B and apossible diameter of opening 109.

FIG. 5B side view 525 is provided to illustrate the different topography512 that is available to front sprocket assembly 100. In one embodiment,the topography 512 of front sprocket assembly 100 is not flat, but is ofdifferent thicknesses. In one embodiment, the different thicknessincreases the lateral stiffness of front sprocket assembly 100 ascompared to a pressed or flat front sprocket assembly design.

In a bicycle, such as a mountain bike that has a lot of gears in therear, there can be a significant amount of cross-chaining. That is, whenthe chain moves to the outside gears on the rear, there can be anincreasing component of lateral pull on the composite front sprocketassembly 100. In one embodiment, the increase in lateral stiffness dueto the varying topography 512 of composite front sprocket assembly 100will provide additional support against the lateral pull on the frontsprocket assembly 100 that is encountered due to the angle of the chainas different gears are selected.

FIG. 5C cross sectional view 550 provides a look at the differentcomponents of front sprocket assembly 100 as they are formed into anirremovably coupled front sprocket assembly 100.

Referring now to FIGS. 6A, 6B, 6C, 6D, 6E, and 6E, are different viewsof outer assembly 102 is shown in accordance with an embodiment. Theviews include FIG. 6A front view 600, FIG. 6B front view 605, FIG. 6Cside view 625, FIGS. 6D and 6E sectional views 650, and FIG. 6F detaildrawing 675.

In one embodiment, FIG. 6A front view 600 shows the taper aspects of theplurality of tabs 110 as they grow wider from the inner perimeter ofouter assembly 102 toward the center thereof. That is, FIG. 6A frontview 600 illustrates the tapered shape of tab 110 to include a narrowerlength at a first portion (e.g., the base of tab 110) connected with theinner perimeter of outer assembly 102 and a wider length at a secondportion (e.g., the tip of tab 110) furthest from the inner perimeter ofouter assembly 102.

FIG. 6B front view 605 illustrates a number of weight saving holes 612that are within outer assembly 102. FIG. 6C side view 625 illustratesthe flatness and the thickness, of one embodiment, of outer assembly102. FIGS. 6D and 6E section views 650 also illustrate a number ofdesign differences about outer assembly 102 which may be used for weightsavings, structural rigidity, and the like. FIG. 6F detail drawing 675illustrates one embodiment of the possible geometry, including height,width, chain well, and the like, for the teeth 104 of outer assembly102.

Referring now to FIG. 7, a flowchart 700 of a method for manufacturingthe front sprocket assembly 100 is shown in accordance with anembodiment.

With reference now to 702 of FIG. 7 and FIG. 6, one embodiment receivesan outer assembly 102 comprised of a first material. In one embodiment,the first material is aluminum. However, in another embodiment, thefirst material may be another metal such as, titanium, steel, nickel, orthe like.

With reference now to 710 of FIG. 7 and FIGS. 2 and 3, one embodimentforms a composite center assembly 106 about an inner portion of theouter assembly 102. In one embodiment, center assembly 106 is formed byinjection molding of carbon fiber reinforced nylon. In anotherembodiment, center assembly 106 is formed via compression molding. Inyet another embodiment, center assembly 106 is formed via compositelayering.

With reference now to 712 of FIG. 7 and FIGS. 2 and 3, in one embodimentthe composite center is comprised of a second material. In oneembodiment, the material for center assembly 106 is a chopped carbonfiber reinforced with nylon. In other embodiments, the material forinjection molded center assembly 106 is chopped carbon fibers. In yetanother embodiment, center assembly 106 may be a plastic, polymer, orthe like. Although a number of specific measurements are referred to, inone embodiment, the length of the chopped carbon fibers may be longer orshorter than 7 mm.

With reference now to 714 of FIG. 7 and FIGS. 2 and 3, in one embodimentthe composite center assembly 106 is disposed at least partially withinthe outer assembly 102.

With reference now to 716 of FIG. 7 and FIGS. 2 and 3, in one embodimentthe composite center is irremovably coupled with the outer assemblywithout using an external fastening device. For example, as describedherein, center assembly 106 may be manufactured via composite layeringor the like which would allow center assembly 106 to be irremovablycoupled with and have a continuous perimeter about outer assembly 102without the concern of knit line formation.

In another embodiment, center assembly 106 includes a plurality of tabs110 on the inner perimeter and center assembly 106 is irremovablycoupled to outer assembly 102 utilizing tabs 110 of outer assembly 102such that center assembly 106 is formed about tabs 110 of outer assembly102, e.g., via injection molding, pressure molding, or the like. In oneembodiment, tabs 110 are tapered such that they are narrower at the baseof outer assembly 102 and wider at the furthest point from outerassembly 102. As such, the center assembly 106 will lock about the tabs110 of outer assembly 102 and resist having outer assembly 102 frombeing pulled out of the center assembly 106.

With reference now to FIG. 8, a flowchart 800 of a method formanufacturing the front sprocket assembly 100 that includes crank drivering 108 is shown in accordance with an embodiment. The portions offlowchart 800 are utilized in addition to those previously described inflowchart 700 such that an additional component, crank drive ring 108,is also irremovably coupled into the composite front sprocket assembly100 during the formation thereof.

Referring now to 802 of FIG. 8 and also FIGS. 1 and 4, one embodimentreceives the optional crank drive ring 108. In one embodiment, the innerdiameter of crank drive ring 108 includes a geometry that corresponds tothe shape of front sprocket assembly interface 17. The outer diameter ofcrank drive ring 108 has an array of block features 401 that aresurrounded by partial holes 415 which are slightly over-center

As described herein, crank drive ring 108 is used to transfer the loadduring high pressure situations, and to stop brinelling that may occurin the composite material of center assembly 106 along the splineinterface and marring about opening 109. In one embodiment, the crankdrive ring 108 is made of the same material as outer assembly 102. Inanother embodiment, the crank drive ring 108 is made of a differentmaterial such as titanium, steel, or other metal or composite. In oneembodiment, crank drive ring 108 is ceramic. For example, a ceramicco-mold may be used to mold a ceramic crank drive ring 108 within theinjection mold process that forms composite front sprocket assembly 100.

With reference now to 810 of FIG. 8 and also FIGS. 2 and 3, oneembodiment orients the crank drive ring 108 within a perimeter of theouter assembly 102 such that the crank drive ring 108 is disposed aboutan approximate center of the outer assembly 102.

Referring now to 812 of FIG. 8 and also FIGS. 2 and 3, one embodimentforms the composite center assembly 106 about the inner portion of theouter assembly 102 and an outer portion of the crank drive ring 108. Inone embodiment, center assembly 106 is formed by injection molding ofcarbon fiber reinforced nylon. In another embodiment, center assembly106 is formed via compression molding. In yet another embodiment, centerassembly 106 is formed via composite layering.

Referring now to 814 of FIG. 8 and also FIGS. 2 and 3, in one embodimentthe composite center assembly 106 is disposed at least partially aboutan external perimeter of the crank drive ring 108.

With reference now to 816 of FIG. 8 and also FIGS. 2 and 3, in oneembodiment the composite center is irremovably coupled with the crankdrive ring without using an external fastening device. As describedherein, in one embodiment, the outer diameter of crank drive ring 108has an array of block features 401 that are surrounded by partial holes415 which are slightly over-center to create a tapered shape on theblock features 401 that acts similar to a shrink fit for locking thecrank drive ring 108 into the composite center assembly 106.

Thus, embodiment of the front sprocket assembly 100 described hereinachieve a more integrated aesthetic with carbon crank arms.Additionally, embodiments create a front sprocket assembly 100 which islighter than all-aluminum front sprockets. For example, in oneembodiment, the target weight of front sprocket assembly is 60 grams.Moreover, the front sprocket assembly 100 is able to achieve the aboveaccomplishments while still meeting or exceeding conventional strengthand stiffness criteria for front sprockets. E.g., the fatigue liferequirements dictated by JIS D 9415-1993, part 4 (5); EN 14766:2005: E,part 4.13.7.X; and ISO 4210-8:2014, Part 4.4.1. Also, the front sprocketassembly 100 can be built with a lower cost than is found in manyconventional front sprockets.

The foregoing Description of Embodiments is not intended to beexhaustive or to limit the embodiments to the precise form described.Instead, example embodiments in this Description of Embodiments havebeen presented in order to enable persons of skill in the art to makeand use embodiments of the described subject matter. Moreover, variousembodiments have been described in various combinations. However, anytwo or more embodiments could be combined. Although some embodimentshave been described in a language specific to structural features and/ormethodological acts, it is to be understood that the subject matterdefined in the appended claims is not necessarily limited to thespecific features or acts described above. Rather, the specific featuresand acts described above are disclosed by way of illustration and asexample forms of implementing the claims and their equivalents.

What we claim is:
 1. A method for forming a bicycle front sprocketassembly, said method comprising: receiving a outer assembly comprisedof a first material; and forming a composite center about an innerportion of said outer assembly, said composite center being comprised ofa second material, said composite center being disposed at leastpartially within said outer assembly, and said composite center beingirremovably coupled with said outer assembly without using an externalfastening device.
 2. The method of claim 1, wherein said outer assemblyis aluminum and said composite center is carbon fiber.
 3. The method ofclaim 1 further comprising: receiving said outer assembly having aplurality of tabs on an inner perimeter thereof; and forming saidcomposite center about said plurality of tabs, said composite centerbeing irremovably coupled with two or more of said plurality of tabs onthe inner perimeter of said outer assembly.
 4. The method of claim 1further comprising: injection molding said second material to form thecomposite center about the inner portion of the outer assembly.
 5. Themethod of claim 1 further comprising: compression molding said secondmaterial to form the composite center about the inner portion of theouter assembly.
 6. The method of claim 1 further comprising:mechanically assembling said second material to form the compositecenter about the inner portion of the outer assembly.
 7. The method ofclaim 1 further comprising: receiving a crank drive ring; orienting saidcrank drive ring within a perimeter of said outer assembly such thatsaid crank drive ring is disposed about an approximate center of saidouter assembly; and forming the composite center about the inner portionof said outer assembly and an outer portion of said crank drive ring,said composite center being disposed at least partially about anexternal perimeter of said crank drive ring, and said composite centerbeing irremovably coupled with said crank drive ring without using anexternal fastening device.
 8. The method of claim 7, wherein said crankdrive ring is aluminum.
 9. The method of claim 7, wherein said crankdrive ring is ceramic.